Heating, ventilating, and air-conditioning (HVAC) systems have been used to maintain desirable temperatures and humidity levels within buildings, and buildings have been constructed with ventilation systems including HVAC systems to provide comfortable and safe environments for occupants to live and work. To maintain fresh air within buildings and to reduce the level of indoor air contaminants, in many applications, at least a portion of the air handled by ventilation or HVAC systems has been taken from outdoors, while a portion of the indoor air handled by HVAC systems has been exhausted to outside the building.
In many situations, outside air introduced to the building to replace exhaust air must be cooled or heated before being introduced to the building to provide temperatures within desired parameters, and often must be dehumidified or humidified in order to keep humidity levels within desired ranges. But adding or removing heat or humidity (moisture) typically involves the expenditure of energy. To reduce the energy required to condition the outside air, recovery wheels have been used to transfer heat, moisture, or both, between exhaust air and incoming outside air. Examples of the prior art in these areas are described in U.S. Pat. Nos. 4,769,053 and 6,199,388, and U.S. Patent Application publication number 2004/0000152, all having at least one inventor in common with the subject matter of this. These prior art documents also describe many of the needs and benefits of such systems and the use of recovery wheels.
Even with recovery devices such as recovery wheels, HVAC systems still use a considerable amount of energy, including both for moving air (fan power) and further conditioning of supply air. To further reduce energy consumption, HVAC systems have been developed that reduce airflow when less flow is needed (variable air-volume systems). In many applications, variable-frequency drive systems have been provided for fan motors, with variable-speed controllers, to reduce fan speeds when full air volume is not needed. Variable voltage DC drives are another option. In some cases, a number of fans are used, and a portion of the fans are shut off when less flow is needed rather than (or in addition to) varying the speed of the fans. Variable air-volume systems have been used that reduce fan power required, that reduce the volume of outside air that must be conditioned, or both.
Further, in some situations, outside air is at a temperature such that the building can be cooled by introducing a higher percentage of unconditioned outside air or “free cooling”, for example, rather than cooling air returned from the space using mechanical cooling (e.g., compressors). HVAC systems have been used having such an economizer wherein outside air is increased when appropriate to reduce energy consumption. Still further, ventilating units have been contemplated that combine a recovery wheel and an economizer. Such units and systems, however, used a return air damper to regulate or modulate flow of return air from the building in order to have the desired amount of outdoor air. Such prior art units and systems, however, required considerable fan energy to pull air through the return air damper. In addition, prior art units and systems have included economizers, but under certain conditions, economizer operation has resulted in supply air that has an undesirable level of humidity, making occupants uncomfortable even when indoor air temperature is within parameters.
Various needs, potential areas for benefit, or opportunities for improvement exist, for example, for ventilating units, HVAC units, energy recovery and economizer modules, and methods that reduce fan energy requirements in one or more modes of operation, that reduce or eliminate the need for a return air damper to regulate or modulate flow of return air from the building in order to have the desired amount of outdoor air, that avoid providing an undesirable level of humidity during economizer operation, or a combination thereof. Further, needs, potential areas for benefit, or opportunities for improvement exist, for example, for ventilating units, HVAC units, energy recovery and economizer modules, and methods that reduce fan energy requirements in multiple modes of operation, for example, when outdoor airflow rates change, for instance, during economizer operation, when total system airflow rates change to meet cooling demands, or both. Further still, needs, potential areas for benefit, or opportunities for improvement exist, for example, for ventilating units, HVAC units, energy recovery and economizer modules, and methods that avoid operating the economizer, and instead provide energy recovery, when outdoor air humidity, enthalpy, or dew point is excessive, or when certain thresholds for comfort are not met. Room for improvement exists over the prior art in various areas that may be apparent to a person of ordinary skill in the art having studied this document.